The present invention relates to an assay using specific binding, for example, an immunoassay, also referred to as immunochromatography.
Currently, there are analytical devices based on the principle of immunochromatography for simple diagnoses of infectious diseases. These analytical devices have better operability and enable measurement in a shorter time, compared to a variety of other conventional testing devices and kits. However, completely satisfactory sensitivity is not yet achieved, and measurement is not possible for some items.
The methods utilizing an immunoassay that have been proposed comprise the steps of applying a sample onto a part of a test piece; allowing the sample to penetrate and infiltrate the test piece using a liquid to reach a detection area of the piece; fixing an analyte contained in the sample to a specific binding reagent immobilized on the detection area of the test piece while the sample is passing through the detection area; and determining the fixed analyte using a labeled reagent. Specific examples of the prior art using this principle are described in GB1589234 of TYROID DIAGNOSTICS INC., and EP022505 of BOOTS-CELLTECH DIAGNOSTICS LIMITED.
An improved technique has been proposed that is based on the above technique and comprises the steps of providing a porous member having a specific substance immobilized on a detection zone and a labeled reagent within a hollow casing made of a moisture-impermeable material; allowing a liquid sample to reach the detection zone while first reacting with the labeled reagent, and to form a complex with the immobilized specific substance; and determining the degree of the binding (Japanese Patent Examined Publication (kokoku) No. 7-46107: Unilever N.V. (NL)).
This proposal is clearly superior to the prior art in that the proposed method can provide a more rapid and convenient analysis, and in particular, it is appropriate for domestic use. This is achieved by placing a test piece within a hollow casing wherein an analyte and a labeled reagent, while reacting with each other, migrate in a porous material by capillary action to reach a detection zone, whereby reacting with the specific binding substance immobilized on the detection zone. However, further improvement is expected because all the reactions are performed simultaneously in a one-step process, so that the labeled reagent is easily affected by an excess amount of reactants and reaction-interfering substances.